The present invention is applied to image forming apparatuses such as a printer, a copy machine, and a facsimile which form images on sheets by such processes as printing and transfer, and more specifically relates to a feeder which separates stacked sheets into individual sheets in order and carries sheets to an image forming section.
Conventionally, in a feeder of an image forming apparatus, an arrangement in which a feeding cassette storing sheets for image formation is detachably provided with respect to an image forming apparatus body has been mainly used. However, such a structure of a detachable feeding cassette inevitably increases the height of the image forming apparatus.
Recently, in image forming apparatuses such as an ink-jet printer for small volume printing, a fixing type feeding cassette which utilizes a bottom plate of the image forming apparatus body as a bottom plate of the feeding cassette tends to be installed instead of the detachable feeding cassette. Compared with the detachable type, the fixing type can store fewer sheets, but the fixing type has an advantage that the height of the image forming apparatus can be decreased.
However, in the fixing type, because it is fixed, problems which did not occur in the detachable type are brought about. That is, unlike the detachable type feeding cassettes which can classify sheets according to size and type of the sheets to some extent by the feeding cassette and can fix feeding conditions in a predetermined range, the fixing type feeding cassette need to solely cope with various sheets which differ in size, thickness, and surface smoothness, etc. Thus, feeding conditions need to be fixed with respect to every kind of sheet used in the feeder. The feeding conditions include a sheet transport power for feeding and transport sheets out of the feeding cassette, and sheet separating power for separating the sheets into individual sheets.
An arrangement of a conventional feeder using the fixing type feeding cassette is shown in FIG. 7.
As shown in FIG. 7, a bottom plate of a fixing type feeding cassette 50 makes up a bottom 57 of an image forming apparatus body, and a sheet lifting plate 59 which pushes up an end of stacked sheets S stored in the feeding cassette 50 is provided on the bottom plate 57. The sheet lifting plate 59 rises by switching off a solenoid 58, so that a front end of the sheets S stacked on the sheet lifting plate 59 is pushed against a feeding roller 51.
The feeding roller 51 is provided along a body frame 54, which is also a right side wall of the image forming apparatus, and a roller section of the feeding roller 51 is divided into plural rollers and provided on a shaft 51a which stretches from the front side to the rear side (see FIG. 4, an explanatory drawing of the present invention in which the feeding roller is indicated by reference number 5 and the roller section is divided into four rollers in FIG. 4).
Further, a sheet separating section for preventing transport of plural sheets S is provided below the feeding roller 51, downstream with respect to a position where a front end of the sheets S is pressed against. The sheet separating section is made up of a separating unit 52 which is provided for each of the divided rollers of the feeding roller 51.
The separating unit 52 includes a separating pad 55 thereon, and the separating pad 55 is pressed against the feeding roller 51. The separating unit 52 is fixed on the body frame 54 via a mounting fraction 52a with a bolt 60, and pushed along a guide rib 53 provided straight up on the bottom plate 57 of the image forming apparatus in a direction shown by an arrow e by a spring 56 whose end is fixed on the bottom plate 57. The separating pad 55 above the spring 56 is pressed against the feeding roller 51 by the pushing force of the spring 56. Here, the guide rib 53 restricts a direction of pressure in pressing the separating pad 55 against the feeding roller 51.
In this arrangement, in feeding sheets, the sheet lifting plate 59 rises by switching off the solenoid 58 and a front end of the sheets S is pressed against the feeding roller 51, so that the sheets S in the feeding cassette 50 are pulled out by rotation of the feeding roller 51 and carried between the feeding roller 51 and the separating pad 55. Here, if plural sheets S are pulled out together one over another, the plural sheets cannot pass between the feeding roller 51 and the separating pad 55 pressed against the feeding roller 51, and the sheets are separated into individual sheets to prevent transport of plural sheets. A sheet S having passed through between the feeding roller 51 and the separating pads 55 is carried to an image forming section (not shown) in accordance with the rotation of the feeding roller 51.
However, the arrangement in which a feeder employs a conventional fixing type feeding cassette brings about problems as follows.
1) In the conventional arrangement, since the separating pad 55 is pressed against the feeding roller 51 all the time, a pressed surface of the separating pad 55 tends to wear out easily. Thus, durability of the separating pad 55 is inferior. As a result, steady sheet separating power can not be maintained and steady sheet feeding over extended periods of time can not be realized.
2) In the conventional arrangement, since the separating unit 52 which includes the separating pad 55 is fixed on the body frame 54 with the bolt 60, it is difficult to displace the separating pad 55. Besides, the spring 56 for providing enough pressure to press the separating pad 55 against the feeding roller 51 to separate sheets exerts pressure diagonally with respect to a direction normal to the separating pad 55. Thus, the spring 56 used to press the separating pad 55 against the feeding roller 51 has pushing force greater than it the pressure required to separate sheets. Therefore, even if a thickness of a sheet S passing through between the separating pad 55 and the feeding roller 51 exerts such a force that a space between the separating pad 55 and the feeding roller 51 would be spread, the separating pad 55 is not separated from the feeding roller 51 and the space between them is hardly changed.
As a result, when sheets S are thin sheets of paper, it is easy to separate plural sheets into individual sheets, but when the sheets S are thick sheets of paper such as post cards, the thickness of the sheets S becomes so thick when they are transported together one over another that stronger pressure than needed is given to the sheets S. Thus, while the sheets can be separated into individual sheets, a front end of the separated sheet S is rolled up or is torn. Note that, when pressure of the spring 56 is selected based on thick sheets S such as post cards to prevent the problem which is caused when the thick sheets S are transported together one over another, the pressure required to separate the thin sheets S cannot be obtained, and transport of plural sheets S cannot be prevented.
The first object of the present invention is to provide a feeder of an image forming apparatus which can feed sheets stably over extended periods of time by improving durability of a separating pad. The second object of the present invention is to provide a feeder of an image forming apparatus which is suitable for a feeder having a fixing type feeding cassette and can prevent transport of plural sheets without fail and without impairing sheets carrying performance regardless of type, size, and surface smoothness etc. of fed sheets.
A feeder of an image forming apparatus of the present invention, to achieve the first object, pressure switching means for pressing a separating pad against a feeding roller only when feeding sheets, wherein, when feeding sheets, said pressure switching means presses the separating pad against the feeding roller, and the feeding roller is rotated, so as to separate stacked sheets into individual sheets between the feeding roller and the separating pad and carry the sheets individually to an image forming section.
According to the arrangement, since the pressure switching means presses the separating pad against the feeding roller only when feeding sheets, a pressed surface of the separating pad is hard to wear out, compared with a conventional arrangement in which the separating pad was pressed all the time. Thus, durability of the separating pad can be improved. As a result, stable sheet feeding can be maintained over extended periods of time.
Also, a feeder of an image forming apparatus, to achieve the second object, includes separating pad displacing means for displacing a separating pad in a direction away from a feeding roller according to a thickness of a sheet passing through between the separating pad and the feeding roller, wherein, only when feeding sheets, said separating pad is pressed against said feeding roller, and the feeding roller is rotated, so as to separate stacked sheets into individual sheets between the feeding roller and the separating pad and carry the sheets individually to an image forming section.
According to the arrangement, since the separating pad displacing means displaces the separating pad in a direction away from the feeding roller according to a thickness of a sheet passing through between the separating pad and the feeding roller, an unnecessary increase of pressure brought about by differences in thickness of sheets can be avoided appropriately, in comparison with a conventional arrangement in which the separating pad was hardly displaced. Thus, the pressure of the separating pad can be made in accordance with a thickness of a sheet passing through between the separating pad and the feeding roller.
As a result, regardless of type, size, and surface smoothness of fed sheets, various sheets can be used to separate sheets into individual sheets without fail and without impairing sheet carrying performance, and transport of plural sheets can be prevented. The foregoing arrangement is particularly effective when applied to a feeder having a fixing type feeding cassette which cannot adjust separating pressure according to type or size of sheets and need to separate various sheets appropriately.
Further, a feeder of an image forming apparatus of the present invention, to achieve the first and the second objects includes, a rotatable pressing support base for pressing a separating pad against a feeding roller and for rotating the separating pad so that the separating pad is displaced in a direction away from the feeding roller in accordance with a thickness of a sheet passing through between the separating pad and the feeding roller; and support base moving means for moving the rotatable pressing support base between a standby position where the separating pad is separated from the feeding roller and a pressing position where the separating pad is pressed against the feeding roller, wherein, when feeding sheets, the separating pad is pressed against the feeding roller, and the feeding roller is rotated, so as to separate stacked sheets and carry the sheets individually to an image forming section.
According to the arrangement, since the rotatable pressing support base presses the separating pad against the feeding roller and rotates the separating pad in a direction away from the feeding roller according to a thickness of a sheet passing through between the separating pad and the feeding roller, an unnecessary increase of pressure brought about by differences in thickness of sheets can be avoided appropriately, in comparison with a conventional arrangement in which the separating pad was hardly displaced. Thus, the pressure of the separating pad can be made in accordance with a thickness of a sheet passing through between the separating pad and the feeding roller.
As a result, regardless of type, size, and surface smoothness of fed sheets, various sheets can be used to separate sheets into individual sheets without fail without impairing sheet carrying performance, and transport of plural sheets can be prevented. The foregoing arrangement is particularly effective when applied to a feeder having a fixing type feeding cassette which cannot adjust separating pressure according to type or size of sheets and need to separate various sheets appropriately.
Besides, since the holder moving means moves the rotatable pressing support base between a standby position where the separating pad is separated from the feeding roller and a pressing position where the separating pad is pressed against the feeding roller, the separating pad can be pressed against the feeding roller only when feeding sheets. Therefore, a pressed surface of the separating pad is hard to wear out, compared with a conventional arrangement in which the separating pad was pressed all the time. Thus, durability of the separating pad can be improved. As a result, stable feeding can be maintained over extended periods of time.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.